Shear-viscosity measurements of liquid 3He-4He mixtures near the tricritical point

This dissertation describes the measurements done of (ρnη), the product of the normal fluid density and the shear viscosity, of 3He-4He mixtures. The emphasis of the experiment was on the range of 3He molar concentrations, Χ, between 64% and 74%. Additional concentrations studied included Χ = 0%, 0.1%, 1.1%, and 50%. The cryostat used is described as well as the experimental technique used. The data for pure 4He is compared to previous results obtained respectively by Bruschi, Biskeborn, and Wang. The data is compared with theory work done by Ferrell in the normal phase, and by Schloms and Dohm in both the normal and superfluid phases. The two dilute mixtures, 0.1% and 1.1%, extended the range of attainable temperatures to colder values by decreasing the superfluid heat leak along the capillary. These data are compared to viscosity data of pure 4He from Heikkila, Stass, Tough, Woods, and Zinov'eva. The 50% mixture provided a second concentration for comparison with data by Wang and allowed us to check for dissipative modes observed by Wang for Χ ≥ 20%. Data for a systematic survey of mixtures near the tricritical point (Χt = 0.675 and Tt = 0.867K) is also presented showing the absence of a weak singularity in η, unlike the behavior near the liquid-vapor critical line of mixtures. The viscosity of these mixtures is dominated by the background viscosity of the Fermi liquid 3He approximately 1.3K. This manifests itself by an increasing trend in η for decreasing temperature in this range